The purpose of this study is to document the effects of pH on newborn hemoglobin-oxygen affinity. Cord blood of acidotic newborns with acute fetal distress during labor and delivery will be studied to evaluate acute adaptations to intrauterine hypoxia and acidosis. The effects of rapid pH changes from acidosis to alkalosis caused by hyperventilation will also be studied in a group of newborns with persistent pulmonary hypertension.